The first approach employed transgenic mice expressing human ACE2 (hACE2).[255] Transgenic hACE2 mice were able to mimic the infectivity of SARS‐cell entry observed in primary hosts.[35, 38, 256, 257] Infection of hACE2‐transgenic mice with TCID50 SARS‐2 doses of 3 × 104 and 7 × 105 resulted in 50% and 100% lethality, respectively, by fifth day post‐infection (n = 4–6). Here, ACE2 is linked to infection.